reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/commit/?id=40e2f9c26033f9859246cfbc7bdbefe981c6ee8e
        git remote add tglx-devel https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git
        git fetch --no-tags tglx-devel timers/ptp/tkntp
        git checkout 40e2f9c26033f9859246cfbc7bdbefe981c6ee8e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash